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Past decades have experienced a plethora of computational studies and with the recent advancements in the computing power; such studies can sometimes be even more efficient than running an experiment in a Laboratory. Computer simulations in molecular scales are performed to bridge the gap between theoretical studies and experiments. Dissipative Particle Dynamics (DPD) which is essentially a Coarse-Grained particle based technique is one of the most promising computer simulation methods in the meso-scales. In DPD each particle represents a group of atoms that are lumped together. Tuning the interaction potential between the particles allows capturing the chemical and physical properties of different types of systems. In this thesis, we first explain the fundamentals of the simulation method, then DPD is used to model polymers and composites. In the first chapter, we focus on the effect of the thermostating technique on proper reproduction of the dynamics of polymer melts. This chapter is followed by a pure DPD investigation of linear viscoelastic properties of polymer chains in entangled and un-entangled regimes. More specifically we will modify the model in order to capture the Rouse to Reptation transition due to the entanglements. A systematic study of the deterministic factors for morphology developments in mixtures of polymers with bare and chemically modified nano-rods is presented in chapter three. A three dimensional phase diagram that includes the effect of both enthalpic and entopic effects is mapped for nano-rod dispersion/aggregation in a polymer matrix. In chapter four, with an inspiration from nature we propose a model for capturing the stimuli responsive behavior of a specific polymer system. Thermo-responsive polymer composites are computationally modeled using an extension of DPD with energy conservation capability. The final chapter of the thesis presents a preliminary study on the interfacial arrangement of double-faced "Janus" particles. Interfacial arrangement of Janus particles is found to be crucial for modifying the morphology and properties of multi-phase systems. Thus in the last chapter of this thesis we briefly study the effect of interface properties and the particle characteristics on their interfacial self-assembly.
This book presents the main results obtained by different laboratories involved in the research group Rheology for polymer melt processing which is associated with French universities, schools of engineering, and the CNRS (Centre National de la Recherche Scientifique - France). The group comprises some 15 research laboratories of varied disciplines (chemistry, physics, material sciences, mechanics, mathematics), but with a common challenge viz. to enhance the understanding of the relationships between macromolecular species, their rheology and their processing. Some crucial issues of polymer science have been addressed: correlation of viscoelastic macroscopic bulk property measurements and models, slip at the wall, extrusion defects, correlation between numerical flow simulations and experiments. Features of the book: • The book is unique in that it allows one to grasp the key issues in polymer rheology and processing at once through a series of detailed state-of-the-art contributions, which were previously scattered throughout the literature. • Each paper was reviewed by experts and the book editors and some coordination was established in order to achieve a readable and easy access style. • Papers have been grouped in sections covering successively: Molecular dynamics, Constitutive equations and numerical modelling, Simple and complex flows. • Each paper can be read independently. Since the book is intended as an introduction to the main topics in polymer processing, it will be of interest to graduate students as well as to scientists in academic and industrial laboratories.
Filling a gap in the literature and all set to become the standard in this field, this monograph begins with a look at computational viscoelastic fluid mechanics and studies of turbulent flows of dilute polymer solutions. It then goes on discuss simulations of nanocomposites, polymerization kinetics, computational approaches for polymers and modeling polyelectrolytes. Further sections deal with tire optimization, irreversible phenomena in polymers, the hydrodynamics of artificial and bacterial flagella as well as modeling and simulation in liquid crystals. The result is invaluable reading for polymer and theoretical chemists, chemists in industry, materials scientists and plastics technologists.
This book is the first to introduce a mesoscale polymer simulation system called OCTA. With its name derived from "Open Computational Tool for Advanced material technology," OCTA is a unique software product, available without charge, that was developed in a project funded by Japanese government. OCTA contains a series of simulation programs focused on mesoscale simulation of the soft matter COGNAC, SUSHI, PASTA, NAPLES, MUFFIN, and KAPSEL. When mesoscale polymer simulation is performed, one may encounter many difficulties that this book will help to overcome. The book not only introduces the theoretical background and functions of each simulation engine, it also provides many examples of the practical applications of the OCTA system. Those examples include predicting mechanical properties of plastic and rubber, morphology formation of polymer blends and composites, the micelle structure of surfactants, and optical properties of polymer films. This volume is strongly recommended as a valuable resource for both academic and industrial researchers who work in polymer simulation.
Advancements in computer simulations have led to their application in understanding structure-property relations of polymer melts and solutions. Friction coefficient and entanglement length are two fundamental parameters in modern tube-based theories. In this work, we use molecular dynamics simulations to study the impact of chain architecture and orientation on these two properties. Multiple scaling arguments have been proposed to describe how the entanglement molecular weight depends on polymer architecture and concentration. Such scaling arguments are well supported either by experiments or through simulation data. Each of these arguments makes certain assumptions, which limits their range of validity. Here, we use simulations to explore a wide range of entangled bead-spring ring chains, to find out how entanglement properties vary with chain stiffness and concentration. We quantify entanglement using three techniques: chain shrinking to find the primitive path, measuring the tube diameter by the width of the "cloud" of monomer positions about the primitive path, and directly measuring the plateau modulus. As chain stiffness varies, we observe three distinct scaling regimes, suggestive of the Lin-Noolandi scaling, semiflexible chains, and stiff chains. The packing length p figures prominently in scaling predictions of the entanglement length and bulk modulus for polymer melts and solutions. p has been argued to scale as the ratio of chain displaced volume V and mean square end-to-end distance R^2. This scaling works for several cases; however, it is not obvious how to apply it to chains with side groups, and the scaling must fail for sufficiently thin, stiff chains. In this work, we measure the packing length in simulations, without making any scaling assumptions, as the typical distance of closest approach of two polymer strands in a simulated bead-spring melt using inter-molecular radial distribution functions. While predicting entanglement length has been the focus of several scaling arguments and simulation studies, understanding the behavior of friction coefficient has received less attention. The monomer friction coefficient [zeta] is known to vary with monomer structure, solvent, and concentration; its variation with chain conformation is less well known and appreciated. We explore the decrease of friction coefficient in extensional flow of polymer liquids, during which chains become partially stretched and aligned. In the second half of this dissertation, we use molecular dynamics simulations to investigate the phase behavior of polyelectrolyte complex coacervates. When oppositely charged polyelectrolytes mix in an aqueous solution, associative phase separation gives rise to coacervates. Experiments reveal the phase diagram for such coacervates, and determine the impact of charge density, chain length and added salt. We propose an idealized model and a simple simulation technique to investigate coacervate phase behavior and show the impact of added salt using a phase diagram. Most studies understanding the phase behavior of polyelectrolyte complex coacervates focus on symmetric mixtures of oppositely charged polymers. This is very rare in biological coacervates. Mixing ratio plays an important role in stability of complexes and applications of such coacervates. We use our idealized simulation model to study the impact of charge-asymmetry on the phase behavior of coacervates.
This extensive and comprehensive collection of lectures by world-leading experts in the field introduces and reviews all relevant computer simulation methods and their applications in condensed matter systems. Volume 2 offers surveys on numerical experiments carried out for a great number of systems, ranging from materials sciences to chemical biology, including supercooled liquids, spin glasses, colloids, polymers, liquid crystals, biological membranes and folding proteins.
Keywords: entanglement, polymer, tube model, molecular dynamics simulation, hard chain model, reptation.
Experts in rheology and polymer processing present up-to-date, fundamental and applied information on the rheological properties of polymers, in particular those relevant to processing, contributing to the physical understanding and the mathematical modelling of polymer processing sequences. Basic concepts of non-Newtonian fluid mechanics, micro-rheological modelling and constitutive modelling are reviewed, and rheological measurements are described. Topics with practical relevance are debated, such as linear viscoelasticity, converging and diverging flows, and the rheology of multiphase systems. Approximation methods are discussed for the computer modelling of polymer melt flow. Subsequently, polymer processing technologies are studied from both simulation and engineering perspectives. Mixing, crystallization and reactive processing aspects are also included. Audience: An integrated and complete view of polymer processing and rheology, important to institutions and individuals engaged in the characterisation, testing, compounding, modification and processing of polymeric materials. Can also support academic polymer processing engineering programs.